Effect of extra-framework Al formed by successive steaming and acid leaching of zeolite MCM-22 on its structure and catalytic performance

Seed‐Assisted Synthesis of MWW‐Type Zeolite with Organic Structure‐Directing Agent‐Free Na‐Aluminosilicate Gel System

“…[54] Both Na-and H-form products exhibit relativelys maller microporev olumes as comparedt ot he seeds, and the following reasons can be considered. [55] reported that the presenceo f extra-framework Al decreased the micropore volume of MCM-22. Mihalyie tal.…”

Transformation of ethylbenzene-m-xylene feed over MCM-22 zeolites with different acidities

“…5A). As was concluded in [19], the generation of EFAl entities by the steaming procedure not only reduces the number of Al-connected proton sites but also causes, most probably, blocking of the zeolite micropores and leads to significant diminish in the adsorption capacity and catalytic activity. It may be inferred from the catalytic data presented above and in accordance to the FT-IR that the Lewis acid sites created upon steam treatment provoke, with the exception of D350/ox, larger m-xylene loss (Fig.…”

“…The FT-IR study combined with the 27 Al-MAS NMR examinations made by us [19], has led to the conclusion that the effect of the dealumination of MCM-22 zeolite on the Al atoms distribution consists in: (i) neutralization of part of the bridging OH groups by cationic extralattice Al species and (ii) partial transformation of the remaining tetrahedral framework Al to tri-coordinated lattice aluminum. These Al rearrangements would suggest substantial change in the zeolite activity.…”

“…The procedure for dealumination [19] at 673 K for 1 h in order to obtain bifunctional Pt/H-zeolite sample.…”

“…In the present work modified MCM-22 zeolites with varying composition of the building lattice elements and diverse number and strength of the acid sites were used for the selective transformation of EB in presence of m-xylene at high temperature and atmospheric pressure. Two methods for modification of this zeolite thoroughly studied by us before [19,20], were applied for moderating the acidity of MCM-22: (i) dealumination by steaming and successive acid treatment and (ii) isomorphous substitution of framework Al for boron.…”